One of the most basic English diacritics, the macron – a single bar (ā) – indicates a long vowel. In most dialects of American English, long vowels are pronounced like each letter’s name, like in cake, Pete, mice, grove, and rule. Conversely, the breve – shaped like the bottom half of a circle (ă) – marks a short vowel, like in cat, bet, fit, rot, and nut. Although these diacritics help with pronunciation, they don’t appear in the actual word.
In English, the grave is sometimes used in poetry to denote an otherwise silent letter should be pronounced – like livèd (pronounced liv-ĕd). The diaresis – two dots above a vowel (ü) – works similarly: the name Zoë might be pronounced as “zō” – the oe spoken as a diphthong (single sound made of two vowels), like in “toe”. The diaresis tells the reader to pronounce the o and e separately, as “zō-ĕ.” The diaresis is sometimes incorrectly omitted from words like Noël and naïve, but some publications (most notably the New Yorker) overuse the diaresis, adding them to words like coöperate and reënter, even though this use is considered archaic.
Germans call the diaresis umlaut; it appears over ä, ö, and ë to change the letters pronunciation is some verbs and plural nouns. These umlauted vowels roughly approximate the sounds in jail, took, and cruel, respectively. Superfluous umlauts appear in Heavy Metal Rock culture (Mötley Crüe or Mötorhead) to suggest the historic strength and boldness of northern European Vikings and Goths. This use is colloquially called metal umlaut or röck döts.
When a diacritic is frequently paired with one letter, it might be considered a separate letter of the alphabet. Consider the tilde, the wavy line that marks the ñ in Spanish loanwords like jalapeño, piñata, and El Niño. Although we see a tilded n, Spanish considers it a separate letter called an eñe, pronounced like the “ny” in canyon.
Tildes are more and more frequently omitted in English – indeed, all diacritics are somewhat endangered. Not only do these slashes and squiggles intimate their native languages, they’re useful. Like punctuation, they’re tools to make language more clear. So the next time you’re tempted to exclude an acute or disregard a diaresis, ask yourself: is it more important to save half a second, or say what you mean as precisely as possible?